Screening and heterologous expression of flavone synthase and flavonol synthase to catalyze hesperetin to diosmetin

Flavonoids as Aglycones in Retaining Glycosidase-Catalyzed Reactions: Prospects for Green Chemistry

Flavonoids and their glycosides are abundant in many plant-based foods. The (de)glycosylation of flavonoids by retaining glycoside hydrolases has recently attracted much interest in basic and applied research, including the possibility of altering the glycosylation pattern of flavonoids. Research in this area is driven by significant differences in physicochemical, organoleptic, and bioactive properties between flavonoid aglycones and their glycosylated counterparts. While many flavonoid glycosides are present in nature at low levels, some occur in substantial quantities, making them readily available low-cost glycosyl donors for transglycosylations. Retaining glycosidases can be used to synthesize natural and novel glycosides, which serve as standards for bioactivity experiments and analyses, using flavonoid glycosides as glycosyl donors. Engineered glycosidases also prove valuable for the synthesis of flavonoid glycosides using chemically synthesized activated glycosyl donors. This review outlines the bioactivities of flavonoids and their glycosides and highlights the applications of retaining glycosidases in the context of flavonoid glycosides, acting as substrates, products, or glycosyl donors in deglycosylation or transglycosylation reactions.

Bioprospecting microbes and enzymes for the production of pterocarpans and coumestans

The isoflavonoid derivatives, pterocarpans and coumestans, are explored for multiple clinical applications as osteo-regenerative, neuroprotective and anti-cancer agents. The use of plant-based systems to produce isoflavonoid derivatives is limited due to cost, scalability, and sustainability constraints. Microbial cell factories overcome these limitations in which model organisms such as Saccharomyces cerevisiae offer an efficient platform to produce isoflavonoids. Bioprospecting microbes and enzymes can provide an array of tools to enhance the production of these molecules. Other microbes that naturally produce isoflavonoids present a novel alternative as production chassis and as a source of novel enzymes. Enzyme bioprospecting allows the complete identification of the pterocarpans and coumestans biosynthetic pathway, and the selection of the best enzymes based on activity and docking parameters. These enzymes consolidate an improved biosynthetic pathway for microbial-based production systems. In this review, we report the state-of-the-art for the production of key pterocarpans and coumestans, describing the enzymes already identified and the current gaps. We report available databases and tools for microbial bioprospecting to select the best production chassis. We propose the use of a holistic and multidisciplinary bioprospecting approach as the first step to identify the biosynthetic gaps, select the best microbial chassis, and increase productivity. We propose the use of microalgal species as microbial cell factories to produce pterocarpans and coumestans. The application of bioprospecting tools provides an exciting field to produce plant compounds such as isoflavonoid derivatives, efficiently and sustainably.

Substrates and Loaded Iron Ions Relative Position Influence the Catalytic Characteristics of the Metalloenzymes Angelica archangelica Flavone Synthase I and Camellia sinensis Flavonol Synthase

Metalloenzymes are a class of enzymes that catalyze through the metal ions they load. Angelica archangelica flavone synthase I (AnFNS I) and Camellia sinensis flavonol synthase (CaFLS), both of which belong to metalloenzymes, have highly similar structures and metal catalytic cores. However, these two enzymes catalyze the same substrate to produce significantly different products. To identify the cause for the differences in the catalytic characteristics of AnFNS I and CaFLS, their protein models were constructed using homology modeling. Structural alignment and molecular docking was also used to elucidate the molecular basis of the differences observed. To analyze and verify the cause for the differences in the catalytic characteristics of AnFNS I and CaFLS, partial fragments of AnFNS I were used to replace the corresponding fragments on CaFLS, and the catalytic characteristics of the mutants were determined by bioconversion assay in E. coli and in vitro catalytic test. The results suggest that the difference in catalytic characteristics between AnFNS I and CaFLS is caused by the depth of the active pockets and the relative position of the substrate. Mutant 10 which present similar dock result with AnFNS I increased the proportion of diosmetin (a flavone) from 2.54 to 16.68% and decreased the proportion of 4′-O-methyl taxifolin (a flavanol) from 47.28 to 2.88%. It was also indicated that the atoms in the substrate molecule that determine the catalytic outcome may be H-2 and H-3, rather than C-2 and C-3. Moreover, it is speculated that the change in the catalytic characteristics at the changes relative spatial position of H-2/H-3 of hesperetin and the loaded carbonyl iron, caused by charged residues at the entrance of the active pocket, is the key factor for the biosynthesis of flavone from flavanone.